What is an enzyme?
Tertiary structure proteins which catalyse reactions (biological catalysts) by lowering activation energy (energy required for reaction)
What is the active site of an enzyme?
- specific and unique in shape due to the specific folded and bonding in the tertiary structure of the protein
- only a substrate that are complementary in shape can bind
How would a change in the primary/ tertiary structure effect enzymes function?
- if a mutation occurs in the gene that determines the primary structure it could change tertiary structure
- if tertiary structure is altered by changes in pH or temp the shape of active site will change so the substrate can’t bind to active site so the enzyme can’t carry out its function
What is the Lock and Key model?
- the shape of the substrate exactly fits into active site of an enzyme as they are complementary in shape
- it is due to random collisions that the substrate can bind to enzyme and for enzyme - substrate complexes
What is a limitation of the Lock and Key model?
the enzyme is rigid but it was later found that it was flexible
What is the induced fit model?
- the enzyme and substrate are not precisely complementary but once the substrate binds to active site they become complementary
- the enzyme is flexible and can mould itself around he substrate
- as it changes shape the enzyme puts strain on the substrate molecule which distorts particular bond/bonds in the substrate and lowers the activation energy needed to break the bonds
How to measure rate of an enzyme reaction?
- how fast product is made
- how fast substrate is broken down
How does temperature affect enzyme reactions?
1.) rate of reaction increases so enzymes and substrates have more kinetic energy to overcome activation energy so there is more chance of successful collisions
2.) optimum temp - enzyme is saturated as occupied by substrate
3.) enzymes denature as the high temp breaks bond holding secondary/ tertiary structure holding the enzymes together which changes the shape of the active site so the substrate can no longer bind
How does the substrate concentration affect rate of enzyme reaction?
- More substrate = more to collide with enzymes to form more enzyme - substrate complexes
- at high concentrations enzyme molecules become saturated with substrate so few enzymes are free so adding more substrate doesn’t affect the rate of reaction
How does pH affect the rate of an enzyme reaction?
If it is too high or too low the pH interferes with the charges in the amino acids in the active site which can break bonds holding tertiary structure together which changes shape of the active site so the enzymes are denatured and fewer enzyme - substrate complexes are formed
How does enzyme concentration affect rate of enzyme reaction?
As long as there is an excess substrate, an increase in amount of enzyme leads to proportionate increase in rate of reaction
- if substrate becomes limiting factor increase in enzymes will have no effect
What is a competitive inhibitor?
Molecule that has a similar structure to normal substrate that can also fit into active site so competes for active site which slows the reaction
- rate of reaction can be normal if substrate conc is incraesed
What is a non competitive inhibitor?
Molecule that binds to another part of enzyme (allosteric site) which changes shape of enzyme including active site do it can no longer bind to substrate which reduces amount of active enzymes
What is a reversible inhibitor?
Binds weakly and can be washed out
What is a irreversible inhibitor?
Binds tightly and cannot be washed out
